This invention relates to a process for producing powdery fillers having hydrophilic properties, said fillers being prepared from crosslinked polymers. The invention also relates to the polymeric product produced by the method and to the novel fillers as well as to uses therefor.
The use of fillers is broadly employed in the plastics processing industry. The addition thereof to plastics gives to the resulting material further desired properties which the starting material does not possess. Thus, for example, impact strength can be substantially enchanced by including fibrous fillers; thermal stability by including mineral fillers and so on. Recently, a certain degree of hydrophility has been required in some types of plastics used as substitutes for natural leather. In the latter case, this means the ability to absorb water vapors at higher concentration in air and to desorb the same rapidly and if possible, quantitatively with a decreased concentration in air. The foregoing rapid sorption and desorption is one of the principal characteristic features of natural leather and is most important from the hygienic standpoint.
Several natural materials occur which possess similar hydrophilic properties such as, for example, wood, cellulose, starch and the like. The sorption capacity of these materials, however, which are also used as fillers, is rather low, i.e., having a range of 15 to 25% of absorbed water vapor calculated on the dry material, which corresponds to a value identical with the sorption of natural leather. Consequently, only very limited progress has been achieved by the application of these materials, as additives, to increase the hydrophility of plastics, even if one ignores the fact that the physical and mechanical properties of the product are sacrificed by the application thereof due to the necessity of the high quantity of filler needed.
Synthetic polymers of the instant invention provide entirely new possibilities for the application disclosed. Their properties, i.e., hydrophility, can be varied over a considerably wide range, i.e., they can be "tailor made". Heretofore, they have not been prepared in a sufficiently fine-grained form such that they appreciably would not influence the appearance of the finished material. In the past, disintegration and grinding have been successful only in part, and then only under rather difficult conditions, i.e., with deep cooling of the ground material by means of liquid nitrogen and the like.
A number of patents have involved the copolymerization of carboxyl-containing monomers with various other monomers, but these patents are non-applicable to our present invention.
U.S. Pat. No. 2,923,692 relates to salts of crosslinked carboxylic polymers, wherein the formed salts are highly swollen mucilage existing only in aqueous medium. They are obtained by the copolymerization of an olefinically unsaturated carboxylic acid with a conjugated unsaturated compound in a hydrocarbon solvent. The conjugated unsaturated compound has a concentration of 0.1 to 10%. This patent does not provide a means for the isolation of the salt from its swollen state in the aqueous medium. Furthermore, at the concentration level of 0.1 to 10% of crosslinking agent, the resulting copolymer is not a solid but rather a gumlike mass which is not suitable as a filler in other polymeric materials.
U.S. Pat. No. 3,586,646 relates to the formation of terpolymers having an acid group thereon, wherein these polymers are used as cation exchange resins. The copolymers of the present invention are not terpolymers.
U.S. Pat. No. 3,530,102 relates to terpolymers formed from maleic anhydride, divinyl benzene and vinyl alkylether; which terpolymers are not related to the salts of the copolymer of the present invention.
Canadian Pat. No. 592,794 relates to the copolymerization of an .alpha.-.beta.-ethylenedicarboxylic acid derivative such as esters with aliphatic conjugated diolefins such as butadiene, which are not capable of crosslinking reactions and therefore the resulting linear polymers are soluble in toluene as clearly defined in the claims. The resulting copolymers are soft tacky masses as clearly shown in the examples, which are not suitable as fillers as are the solid copolymers of the present invention.